Tuned circuit system



March 18, 1941.

INVENTOR- gLTE/Q VAN 5. ROBERTS BY A TTORNEY.

Patented Mar. 18, 1941 UNITED Walter van B.

It is sometimes desirable of an oscillatory circuit, grounded, without in PATENT OFFECE 2,235,565 TUNED CIRCUIT SYSTEM of Delaware Roberts, Princeton, to Radio Corporation of America,

N. 1., assignor a corporation.

Application January "I, 1939, Serial No. 249,749

8 Claims.

to sharpen the tuning one end of which is anyway altering the connections of this circuit or making any extra points of connection to the inductance thereof.

There are a number of known ways for doing this, but most of them involve a drawback of one sort or another. For example, an extra coil having a few turns may be wound in coupling relation to the coil of the oscillatory circuit and utilized as a feed-back coil in one to use plug-in coils, howbe any extra pins provided Where it is desired ever, there may not way or another.

on the form for connection to this extra coil. Also, this extra coil should not have a fixed value, since a fixed coil is not suitable as a feedback coil for a wide variety of different plug-in coils which may be circuit. Similarly,

plugged into the oscillatory a variable inductance in the plate circuit of a vacuum tube is known to produce regeneration in a tuned circuit connected between its grid and cathode. different plug-in coil, it would However, for each be necessary to provide a different value of variable inductance to obtain the desired amount of regeneration.

The primary object of this invention is to provide a simple means for in a resonant circuit, and

producing regeneration especially to provide a means which functions satisfactorily without alteration for a wide variety may be plugged into said A better understanding be had by referring to which is accompanied of different coils that resonant circuit.

of the invention may the following description by a drawing whose single figure shows the invention applied, by way of example only, to the tuned circuit of the first stage of a receiver.

It should be understood,

companying drawing is given merely for the purhowever, that the acpose of exposition and not as a limitation, since the invention is applicable to any tuned circuit Whether it be used in a receiver or in a transmitter, in connection with an amplifier, converter, or detector tube, or merely as a wavemeter without the need of a vacuum tube.

In the drawing, mentary portion of an system of the type which the heavy lines show a fragalready existing receiving includes an antenna and a frequency converter or mixer tube T between whose grid G and cathode K there is connected a parallel tuned resonant circuit l including a plug-in coil system grounded at one end 3. It will be evident that the drawing does not show all essential elements of the frequency converter tube T, such as the means for applying the heterodyne oscillations, since these are not necessary for an understanding of the principles of the invention. Reference numerals A, A designate the terminals of the rep acing plug-in coil L of the resonant circuit, which is in parallel relation to a variable capacitor C.

According to the invention, there is provided an extra vacuum tube T which is an amplifier whose grid G is connected to the ungrounded end of the resonant circuit I while its cathode 10 is connected to ground through a choke coil X whose impedance at the operating frequency is capacitive. The plate P of the tube is grounded for radio frequency variations through a sufficiently large condenser C while its direct current potential is adjustable by means ofpotentiometer P connected between ground and a point of positive potential.

The operation of this arrangement depends upon the existence of inherent capacity between grid G and cathode K of tube T which, together with the effective capacity of choke X, forms a capacity potentiometer across the tuned circuit so that the grid and. plate of the tube T are connected to the ends A, A of the tuned 'cir- 5 cuit, while the potential of the cathode is intermediate the potential of these two ends. The tube T is thus connected to the resonant circuit in the same way as it would be connected in the case of a Colpitts three-point oscillator circuit except that one terminal of the resonant circuit is grounded instead of the cathode being grounded as in the Co-lpitts circuit. This will be apparent from an inspection of the inherent capacities shown in dotted lines. By sliding the connection of potentiometer P from ground toward the positive potential end, the transconductance of the tube T is varied and the effect of the tube T is first to regenerate the circuit l and ultimately to produce oscillations. This arrangement has been found in practice to produce readily controllable regeneration over a wide range of frequencies. It is, of course, possible to supplement the grid-cathode capacity of the tube T or the distributed capacity of the choke X, or both, by auxiliary condensers, but this has not been found necessary in practice and it is preferable not to increase the total capacity shunted across the variable condenser C any more than necessary since this alters the tuning range of 50 the variable condenser.

Although the circuit of the drawing shows the grid G of tube T connected to the upper end or ungrounded side of the resonant circuit I, while the plate P is connected for radio frequency 55 and inherent capacity energy to the lower or grounded end of the resonant circuit, it should be evident that if desired the grid and plate electrodes may be reversed in position without departing from the principles of the invention involved in this circuit arrangement.

The term ground used in the foregoing description and in the appended claims is deemed to include any surface of zero or relatively fixed alternating current potential.

What is claimed is:

1. In combination, a parallel tuned resonant circuit comprising an inductance coil and a capacitor in shunt thereto, a connection from one terminal of said tuned circuit to ground, an electron discharge device having grid, cathode and plate electrodes and inherent capacity between said grid and cathode electrodes, connections of low impedance to radio frequency energy from said grid and plate to opposit terminals of said tuned circuit, a connection including a choke coil having effective capacity reactance at the operating frequency from said cathode to that terminal of said tuned circuit to which said plate is connected, and means for varying the transconductance of said device.

2. In combination, a parallel tuned resonant circuit comprising an inductance coil and 2, capacitor in shunt thereto, a connection from one terminal of said tuned circuit to ground, an electron discharge device having grid, cathode and plate electrodes and inherent capacity between said grid and cathode electrodes, a, direct connection from said grid to the other terminal of said tuned circuit, a connection through a path of low radio frequency impedance from said plate to the grounded terminal of said tuned circuit, a connection including a choke coil having effective capacity reactance at the operating frequency from said cathode to ground, a source of voltage connected between said cathode and plate electrodes, and means for varying the transcon- ;ductance of said device.

3. In combination, a parallel tuned resonant circuit comprising an inductance coil and a capacitor in shunt thereto, a connection from one terminal of said tuned circuit to ground, a utilization circuit connected to the other terminal of said tuned circuit, an amplifier electron discharge device having grid, cathode and plate electrodes and inherent capacity between said grid and cathode electrodes, connections of low impedance to radio frequency energy from said grid and plate to opposite terminals of said tuned circuit, a connection including a choke coil having effective capacity reactance at the operating frequency from said cathode to that terminal of said tuned circuit to which said plate is connected, and a potentiometer for supplying adjustable voltage betweensaid cathode and plate electrodes.

4. In combination, a parallel tuned resonant circuit comprising an inductance coil and a capacitor in shunt thereto, a connection from one terminal of said tuned circuit to ground, a utilization circuit connected to the other terminal of said tuned circuit, an amplifier electron discharge device having grid, cathode and plate electrodes between said grid and cathode electrodes, a connection from said grid to the ungrounded terminal of said tuned circult, and a connection having low impedance to radio frequency energy from the plate to ground, a connection including a choke coil having effective capacity react-lance at the operating frequency from said cathode to ground, and a potentiometer having one terminal grounded and the other terminal connected to a. source of positive potential and a. slidable connection from said potentiometer to said plate.

5. A two-terminal negative operative over a wide range prising a pair of terminals rectly connected to a point current potential, a pair of connected in series between electron discharge device having a grid directly connected to one terminal, a cathode connected to the junction of said capacity reactances, and a. plate connected to the other terminal, means for producing a direct current flow between cathode and plate, and means for adjusting said current with a consequent control .of the negative resistance between said terminals.

*6. A two-terminal negative resistance device operative over a wide range of frequencies comprising a pair of terminals one of which is at a fixed alternating current potential, a variable capacitor directly connected across said terminals, a pair of capacity reactances connected in series between said terminals, an electron discharge device having a grid connected to one terminal, a cathode connected to the junction of said capacity reactances, and a plate connected to the other terminal, means for producing a direct current flow between cathode and plate, and means for adjusting said current with a consequent control of the negative resistance between said termfn'alsl '7. A two-terminal negative resistance device operative over a wide range of frequencies comprising :a pair of terminals one of which is at a fixed alternating current potential, an inductance coil directly connected across said terminals, a pair of capacity reactances connected in series between said terminals, an electron discharge device having a grid connected to one terminal, a cathode connected to the junction of said capacity reactances, and a plate connected to the other terminal, means for producing a. direct current flow between cathode and plate, and means for adjusting said current with a consequent control of the negative resistance between said terminals.

8. A two-terminal negative resistance device operative over a Wide range of frequencies comprising a pair of terminals one of which is at a fixed alternating current potential, a fixed inductance coil shunted by a variable capacitor directly connected across said terminals, a pair of capacity reactances connected in series between said terminals, an electron discharge device having a grid directly connected to one terminal, a cathode connected to the junction of said caa plate connected to the other terminal, means for producing a direct current flow between cathode and plate, and means for adjusting said current with a consequent 'con trol of the negative resistance between said terminals.

resistance device of frequencies comone of which is diof fixed alternating capacity reactances WALTER VAN B. ROBERTS. 

